We wish to determine the relative safety or hazards of possible anesthetic techniques used to facilitate emergency delivery of the stressed asphyxiated fetus. In the pregnant ewe near term we will produce utero-placental insufficiency, partial umbilical cord occlusion or acute maternal hypovolemia. We will study five different anesthetics, each of which produces different cardiovascular responses in the mother and fetus. To assess the relative merits of each anesthetic we will measure maternal and fetal cardiovascular and acid-base status, as well as fetal total and cerebral oxygen consumption, and fetal regional cerebral blood flow. We postulate that in the asphyxiated fetus, that has lost its ability to autoregulate cerebral blood flow, anesthetic agents and adjuvants which maintain or increase fetal blood pressure will produce better fetal cerebral oxygenation. Possibly isoflurane/oxygen may be unique in providing cerebral protection during acute asphyxia. Our long term objective is to suggest anesthetic techniques which will help reduce perinatal morbidity all too often manifested by cerebral palsy and mental retardation.